Tetiana Dychenko

The object of this study was concrete samples of the cathedral and wall frescoes. The study solved the problem related to the destruction of concrete and wall frescoes under the long-term influence of biochemical and climatic factors. Samples of concrete for research and wall murals were obtained from a historic listed building. Using microbiological studies and scanning electron microscopy, damage to wall murals and concrete by microscopic fungi was established: Aspergillus fumigatus, Penicillium brevicompactum, Aspergillus niger, Cladosporium sphaerospermum. The study of concrete samples by the TPD-MS method showed the presence of an increased level of moisture and carbon compounds by 20 % in the test samples, compared to control. The sulfur content in all concrete samples was not significant. Determination of the mineral composition of concrete by X-ray diffraction showed the presence of Al2O3, 36–44 %, which indicates a significant clay content. The presence of NiTi, 53 %, and СoMg7O8, 46 %, in the concrete sample indicates the probable migration of the chemical elements of the paint pigments used to decorate the cathedral. The concrete control sample contained a significant amount of SiO2, up to 51 %, which is the main component of sand. A feature of the work is the determination of the corrosion effect on concrete under prolonged exposure to climatic and biological factors. The present study is distinguished by the use of non-destructive methods: microbiological studies, scanning electron microscopy, TPD-MS and X-ray diffraction to determine the destruction of concrete and wall frescoes of the building, which is a cultural heritage. The results of the study could be applied to the development and planning of restoration works for the restoration of buildings that have historical value

Chromate and dichromate solutions used for the activation and passivation of cadmium and zinc galvanic coatings of metal products are widely used due to their ability to form corrosion-protective films. Therefore, in this article, we examined the kinetic features of the cathodic deposition of Cd and Zn during membrane electrolysis. As a result of comprehensive experimental and theoretical studies, the features of Cd and Zn cathodic depositions were analyzed under different hydrodynamic conditions in a submembrane zone of an anolyte. Experimental physicochemical methods such as the experimental analysis of solutions, analytical modeling, and a statistical analysis were used during the research. A regression dependence for evaluating a reaction rate constant was assessed based on the least-square approximation of the proposed model. As a result, the peculiarities of the cathodic formations for Cd and Zn during the membrane electrolysis process were analyzed. The effect of mechanical mixing with different values of the Reynolds number on the deposition of Cd and Zn on a cathode was evaluated. A change in Cd²⁺ and Zn²⁺ ion concentrations was also considered during the research. Overall, the obtained results increased the Cd deposition rate by 2.2 times using an active hydrodynamic environment with the anolyte.

The work studies the process of Cd2+ and Zn2+ cations transfer through a RALEX (R) CM-PES 11-66 cation-exchange membrane and the cations reduction as metals on the cathodes at the cathode chambers of the electrochemical units with a view to prevent the hydrosphere contamination with the electroplating solutions. Electrolysis of the solutions that imitated the possible composition of the passivating baths contained 50 g/l sodium dichromate, 10 g/l sulfuric acid and impurity ions of Cd2+ and Zn2+ in various concentrations. The designed passivation solutions with certain amount of impurity ions in the colour solution were forcibly mixed. The impact of the impurity ions concentration in the colour solution and of a forced mixing on the metal reduction was studied. Regularity in the increased metal reduction dependent on the metal concentration was found and the conditions favouring the ion migration through the cation-exchange membrane due to forced mixing were defined.